Geopolymer Cement Compositions and Methods of Use

ABSTRACT

Methods and compositions for cementing operations that include pumice in geopolymer cement compositions comprising slag.

BACKGROUND

The present invention relates to cementing operations and, moreparticularly, in certain embodiments, to geopolymer cement compositionscomprising slag and pumice and associated methods use in cementingoperations.

In cementing operations, such as well construction and remedialcementing, cement compositions are commonly utilized. Cementcompositions may be used in primary-cementing operations whereby pipestrings, such as casing and liners, are cemented well bores. In atypical primary-cementing operation, a cement composition may be pumpedinto an annulus between the walls of the well bore and the exteriorsurface of the pipe string disposed therein. The cement composition mayset in the annular space, thereby forming an annular sheath of hardened,substantially impermeable material (e.g., a cement sheath) that maysupport and position the pipe string in the well bore and may bond theexterior surface of the pipe string to the well bore walls. Among otherthings, the cement sheath surrounding the pipe string should function toprevent the migration of fluids in the annulus, as well as protectingthe pipe string from corrosion. Cement compositions also may be used inremedial cementing methods, such as in the placement of plugs, and insqueeze cementing for sealing voids in a pipe string, cement sheath,gravel pack, subterranean formation, and the like. Cement compositionsalso may be used in surface applications, for example, in surfaceapplications.

A particular challenge in cementing operations is the development ofsatisfactory mechanical properties in a settable composition within areasonable time period after placement in the subterranean formation.During the life of a well, the subterranean cement sheath undergoesnumerous strains and stresses as a result of temperature effects,pressure effects, and impact effects. The ability to withstand thesestrains and stresses is directly related to the mechanical properties ofthe settable composition after setting. The mechanical properties areoften characterized using parameters such as compressive strength,tensile strength. Young's Modulus, Poisson's Ratio, elasticity, and thelike. These properties may be modified by the inclusion of additives.

One type of settable composition that has been used heretofore comprisesslag cement, which is typically a blend of Portland cement and slag.Because Portland cement develops compressive strength much more rapidlythan slag, the amount of slag is typically limited to no more than 40%by weight of the slag cement. Drawbacks to slag cement include therelatively high cost of the Portland cement as compared to the slag,which is a waste material. Drawbacks to using higher concentrations ofslag may include the inability for the settable composition to developadequate compressive strength in a reasonable time and ensure thelong-term structural integrity of the cement.

Thus, there exists a need for cement compositions that comprise slagwith enhanced mechanical features that develop adequate compressivestrength for use in cementing operations.

SUMMARY

An embodiment discloses a method of cementing. The method of cementingmay comprise providing a geopolymer cement composition. The geopolymercement composition may comprise a cementitious component consistingessentially of slag and pumice, a hydroxyl source, and water. The methodfurther may comprise allowing the geopolymer cement composition to set.

Another embodiment discloses a method of cementing. The method ofcementing may comprise preparing a dry blend comprising lime and acementitious component comprising slag and pumice. The method furthermay comprise combining the dry blend with water to form a geopolymercement composition. The method further may comprise introducing thegeopolymer cement composition into a subterranean formation. The methodfurther may comprise allowing the geopolymer cement composition to set.

Another embodiment discloses a method of cementing. The method ofcementing may comprise providing a geopolymer cement composition. Thegeopolymer cement composition may comprise a cementitious componentconsisting of slag in an amount in a range of from about 40% to about60% by weight of the cementitious component and pumice in an amount in arange of from about 40% to about 60% by weight of the cementitiouscomponent, wherein the geopolymer cement composition is free of anyadditional cementitious component. The geopolymer cement compositionfurther may comprise hydrated lime in an amount in a range of from about0.1% to about 20% weight of the cementitious component, and water. Themethod further may comprise introducing the geopolymer cementcomposition into a well bore annulus in a subterranean formation duringa primary cementing operation. The method further may comprise allowingthe geopolymer cement composition to set, wherein inclusion of thepumice in the geopolymer cement composition increases the 24-hourcompressive strength of the geopolymer cement composition at 180° F. inan amount of at least about 30% as compared to replacement of the pumicewith additional slag.

Yet another embodiment discloses a geopolymer cement composition. Thegeopolymer cement composition may comprise a cementitious componentconsisting essentially of slag and pumice. The geopolymer cementcomposition further may comprise a hydroxyl source and water.

The features and advantages of the present invention will be readilyapparent to those skilled in the art. While numerous changes may be madeby those skilled in the art, such changes are within the spirit of theinvention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the present invention disclose geopolymer cementcompositions comprising slag, pumice, a hydroxyl source, and water. Oneof the many potential advantages of embodiments of the geopolymercompositions is that including a mixture of slag and pumice may providegeopolymer cement compositions with adequate compressive strengths foruse in subterranean applications despite the increased slag content. Byway of example, the compressive strength of the geopolymer cementcompositions containing the mixture of the slag and pumice may beincreased by at least about 10% in one embodiment, and at least about30% in another embodiment, as compared to the same geopolymer cementcomposition having the pumice replaced with additional slag.Accordingly, embodiments of the geopolymer cement compositions may beused in a variety of subterranean applications where cement compositionsmay be used, including, but not limited to, primary and remedialcementing.

In some embodiments, the geopolymer cement compositions may compriseslag. Slag is generally a by-product in the production of various metalsfrom their corresponding ores. By way of example, the production of castiron can produce slag as a granulated, blast furnace by-product with theslag generally comprising the oxidized impurities round in iron ore.Slag may generally be considered to have cementitious properties, inthat it may set and harden in the presence of a hydroxyl source andwater. The slag may be included in embodiments of the geopolymer cementcompositions in an amount suitable for a particular application. In someembodiments, the slag may be present in an amount in a range of fromabout 40% to about 100% by weight of cementitious components (“bwoc”),for example, about 40%, about 50%, about 60%, about 70%, about 80%,about 90%, or about 100%. Cementitious components include thosecomponents or combinations of components of the geopolymer cementcompositions that hydraulically set, or otherwise harden, to developcompressive strength, including, for example, slag, fly ash, hydrauliccement, and the like. In certain embodiments, the slag may be present inan amount greater than about 40% bwoc, greater than about 50% bwoc,greater than about 60% bwoc, greater than about 70% bwoc, greater thanabout 80% bwoc, or greater than about 90% bwoc.

In some embodiments, the geopolymer cement compositions may comprisepumice. Generally, pumice is a volcanic rock that exhibits cementitiousproperties, in that it may set and harden in the presence of a hydroxylsource and water. The hydroxyl source may be used in combination withthe pumice, for example, to provide sufficient calcium ions for thepumice to set. An example of a suitable pumice is available from HessPumice Products, Inc., Malad City, Id., under the tradename DS-200having an average particle size of less than 20 microns. In someembodiments, the pumice may be present in geopolymer cement compositionsof the present invention in an amount in the range of about 0.1% toabout 60% bwoc. In some embodiments, the pumice may be present in anamount ranging between any of and/or including any of about 0.1%, about5%, about 10%, about 20%, about 30%, about 40%, about 50%, or about 60%.In some embodiments, a total amount of cementitious components in thegeopolymer cement composition may consist essentially of and/or consistof the slag, the pumice, and the hydroxyl source. One of ordinary skillin the art, with the benefit of this disclosure, will recognize theappropriate amount of the pumice to include for a chosen application.

In some embodiments, the geopolymer cement compositions may comprise ahydroxyl source. The hydroxyl source may be included in the geopolymercement compositions to provide hydroxyl groups for activation of theslag and/or pumice, thus providing a cement composition that will reactwith the water to form a hardened mass in accordance with embodiments ofthe present invention. Any of a variety of suitable hydroxyl sources maybe used that are capable of generating hydroxyl groups (OH⁻) whendissolved in the water. Examples of suitable hydroxyl sources includebasic materials, such as sodium hydroxide, sodium bicarbonate, sodiumcarbonate, lime (e.g., hydrated lime), and any combination thereof. Insome embodiments, the hydroxyl source may be present in the geopolymercement compositions in an amount in the range of from about 0.1% toabout 25% bwoc. In further embodiments, the hydroxyl source may beincluded in an amount in the range of from about 1% to about 10% bwoc.

In some embodiments, the geopolymer cement compositions may beessentially free of any additional cementitious materials, such ashydraulic, cements, including, but not limited to, those comprisingcalcium, aluminum, silicon, oxygen, iron, and/or sulfur, which set andharden by reaction with water. Specific examples of hydraulic cementsinclude, but are not limited to, Portland cements, pozzolana cements,gypsum cements, high alumina content cements, silica cements, and anycombination thereof in some embodiments, the Portland cements areclassified as Classes A, C, H, or G cements according to AmericanPetroleum Institute, API Specification for Materials and Testing forWell Cements, API Specification 10, Fifth Ed., Jul. 1, 1990. Inaddition, in some embodiments, the hydraulic cement may include cementsclassified as ASTM Type I, II, or III. In some embodiments, thegeopolymer cement compositions may comprise additional cementitiousmaterials in an amount less than about 1% bwoc and, alternatively, lessthan about 0.1% bwoc. In one particular embodiment, the geopolymercement may be free of any additional cementitious materials.

The water used in embodiments of the geopolymer cement compositions ofthe present invention may include, for example, freshwater, saltwater(e.g., water containing one or more salts dissolved therein), brine(e.g., saturated saltwater produced from subterranean formations),seawater, or any combination thereof. Generally, the water may be fromany source, provided, for example, that it does not contain an excess ofcompounds that may undesirably affect other components in the geopolymercement composition. In some embodiments, the water may be included in anamount sufficient to form a pumpable slurry. In some embodiments, thewater may be included in the geopolymer cement compositions of thepresent invention in an amount in a range of from about 40% to about200% bwoc. In some embodiments, the water may be included in an amountin a range of from about 40% to about 150% bwoc.

In some embodiments, the geopolymer cement compositions may furthercomprise a fluid-loss-control additive. As used herein, the term“fluid-loss-control additive” refers to an additive that is used todecrease the volume of fluid that is lost to the subterranean formation.Examples of suitable fluid-loss-control additives include, but notlimited to, certain polymers, such as hydroxyethyl cellulose,carboxymethylhydroxyethyl cellulose, copolymers of2-acrylamido-2-methylpropanesulfonic acid and acrylamide or N,Ndimethylacrylamide, and graft copolymers comprising a backbone of ligninor lignite and pendant groups comprising at least one member selectedfrom the group consisting of 2-acrylamido-2-methylpropanesulfonic acid,acrylonitrile, and N,N-dimethylacrylamide. Suitable fluid-loss-controladditives are available from Halliburton Energy Services, Inc., underthe tradenames HALAD™-9 fluid-loss additive, HALAD™-23 fluid-lossadditive, HALAD™-344 fluid-loss additive, and HALAD™-413 fluid-lossadditive. In some embodiments, the fluid-loss-control additive may bepresent in the geopolymer cement compositions in an amount in the rangeof from about 0.1% to about 5% bwoc.

In some embodiments, the geopolymer cement compositions may furthercomprise set retarder. As used herein, the term “set retarder” refers toan additive that is used to increase the thickening time of cementcompositions. Examples of suitable set retarders include, but are notlimited to, ammonium, alkali metals, alkaline earth metals, metal saltsof sulfoalkylated lignins, hydroxycarboxy acids, copolymers of2-acrylamido-2-methylpropane sulfonic acid salt and acrylic acid ormaleic acid, and combinations thereof. One example of a suitablesulfoalkylated lignin comprises a sulfomethylated lignin. Suitable setretarding additives are available from Halliburton Energy Services, Inc.under the tradenames HR®-4 cement retarder, HR®-5 cement retarder, HR®-7cement retarder, HR®-12 cement retarder, HR®-15 cement retarder, HR®-25cement retarder, SCR™-100 cement retarder, and SCR™-500 cement retarder.Generally, where used, the set retarder may be included in thegeopolymer cement compositions of the present invention in an amountsufficient to provide the desired set retardation. In some embodiments,the set retarder may be present in the geopolymer cement compositions inan amount in the range of from about 0.1% to about 5% bwoc.

Other additives suitable for use in subterranean cementing operationsmay also be added to embodiments of the geopolymer cement compositions,in accordance with embodiments of the present invention. Examples ofsuch additives include, but are not limited to, strength-retrogressionadditives, set accelerators, weighting agents, lightweight additives,gas-generating additives, mechanical-property-enhancing additives,lost-circulation materials, filtration-control additives, foamingadditives, thixotropic additives, and any combination thereof. Specificexamples of these, and other, additives include crystalline silica,amorphous silica, fumed silica, salts, fibers, hydratable clays,calcined shale, vitrified shale, microspheres, fly ash, diatomaceousearth, metakaolin, ground perlite, rice husk ash, natural pozzolan,zeolite, cement kiln dust, resins, any combination thereof, and thelike. A person having ordinary skill in the art, with the benefit ofthis disclosure, will readily be able to determine the type and amountof additive useful for a particular application and desired result.

Those of ordinary skill in the art will appreciate that embodiments ofthe geopolymer compositions generally should have a density suitable fora particular application. By way of example, embodiments of thegeopolymer cement compositions may have a density of about 12 pounds pergallon (“lb/gal”) to about 20 lb/gal. In certain embodiments, thegeopolymer cement compositions may have a density of about 14 lb/gal toabout 17 lb/gal. Those of ordinary skill in the art, with the benefit ofthis disclosure, will recognize the appropriate density for a particularapplication.

In some embodiments, the geopolymer cement composition may have athickening time of greater than about 1 hour, alternatively, greaterthan about 2 hours, alternatively greater than about 5 hours at 3,000psi and temperatures in a range of from about 50° F. to about 400° F.,alternatively, in a range of from about 80° F. to about 250° F. andalternatively at a temperature of about 140° F. As used herein, the term“thickening time” refers to the time required for a cement compositionto reach 70 Bearden units of Consistency “Bc”) as measured on ahigh-temperature high-pressure consistometer in accordance with theprocedure for determining cement thickening times set forth in APIRecommended Practice 10B-2 (July 2005).

As previously mentioned, the compressive strength of the geopolymercement compositions may be increased by using pumice in combination withslag. Indeed, it has been shown that using pumice in combination withslag can achieve higher compressive strength than use of either pumiceor slag alone. As used herein, the term “compressive strength” refers tothe destructive compressive strength measured in accordance with APIRecommended Practice 10B-2 (July 2005) by physically testing thestrength of the geopolymer cement composition after setting by crushingthe sample in a compression-testing machine. The compressive strength ismeasured at a specified time after the composition has been mixed andthe composition is maintained under specified temperature and pressureconditions. The compressive strength is calculated from the failure loaddivided by the cross-sectional area resisting the load and is reportedin units of pound-force per square inch (“psi”). By way of example, thecompressive strength of the geopolymer cement compositions containingthe mixture of the slag and pumice may be increased by at least about10% in one embodiment and at least about 30% in another embodiment, ascompared to the same geopolymer cement composition having the pumicereplaced with additional slag. In some embodiments, the geopolymercement composition may have a 24-hour compressive strength in a range offrom about 250 psi to about 20,000 psi and, alternatively, from about350 psi about 3,000 psi at atmospheric pressure and temperatures in arange of from about 50° F. to about 400° F., alternatively, in a rangeof from about 80° F. to about 250° F., and alternatively at atemperature of about 180° F.

The components of the geopolymer cement compositions comprising slag,pumice, a hydroxyl source, and water may be combined in any orderdesired to form a geopolymer cement composition that can be placed intoa subterranean formation. In addition, the components of the geopolymercement compositions may be combined using any mixing device compatiblewith the composition, including a hulk mixer, for example. In someembodiments, a dry blend may first be formed by dry blending drycomponents comprising slag, pumice, and a hydroxyl source. The dry blendmay then be combined with water to form the geopolymer cementcomposition. Other suitable techniques may be used for preparation ofthe geopolymer cement compositions as will be appreciated by those ofordinary skill in the art in accordance with embodiments of the presentinvention.

As will be appreciated by those of ordinary skill in the art,embodiments of the geopolymer cement compositions of the presentinvention may be used in a variety of cementing operations, includingsurface and subterranean operations, such as primary and remedialcementing. In some embodiments, a geopolymer cement composition may beprovided that comprises slag, pumice, lime, and water, and allowed set.In certain embodiments, the geopolymer cement composition may beintroduced into a subterranean formation and allowed to set therein. Asused herein, introducing the cement composition into a subterraneanformation includes introduction into any portion of the subterraneanformation, including, without limitation, into a well bore drilled intothe subterranean formation, into a near well bore region surrounding thewell bore, or into both.

In primary-cementing embodiments, for example, embodiments of thegeopolymer cement composition may be introduced into a well-bore annulussuch as a space between a wall of a well bore and a conduit (e.g., pipestrings, liners) located in the well bore, the well bore penetrating thesubterranean formation. The geopolymer cement composition may be allowedto set to form an annular sheath of hardened cement in the well-boreannulus. Among other things, the hardened cement formed by the setgeopolymer cement composition may form a barrier, preventing themigration of fluids in the well bore. The hardened cement also may, forexample, support the conduit in the well bore and/or form a bond betweenthe well-bore wall and the conduit.

In remedial-cementing embodiments, a geopolymer cement composition maybe used, for example, in squeeze-cementing operations or in theplacement of cement plugs. By way of example, the geopolymer cementcomposition may be placed in a well bore to plug an opening, such as avoid or crack, in the formation, in a gravel pack, in the conduit, inthe cement sheath, and/or a microannulus between the cement sheath andthe conduit or formation.

EXAMPLES

To facilitate a better understanding of the present invention, thefollowing examples of some of the preferred embodiments are given. In noway should such examples be read to limit, or to define, the scope ofthe invention.

Example 1

The following series of tests was performed to evaluate the mechanicalproperties of geopolymer cement compositions. Five different geopolymercement compositions, designated Samples 1-5, were prepared using theindicated amounts of water, slag, pumice, and lime. The amounts of thesecomponents are indicated in the table below with percent indicating theamount of the component by weight of the slag and pumice and gallon persack (“gal/sk”) indicating the gallons of the respective component per94-pound sack of slag and pumice. It should be noted that Sample 5 wastoo thick and had to be hand mixed. The slag used was from LaFarge,Grand Chain, Ill. The lime used was hydrated lime from Texas LimeCompany, Cleburne, Tex. The pumice used was DS-200 from Hess PumiceProducts, Inc.

After preparation, the sample geopolymer cement compositions wereallowed to cure for 24 hours in a 2″×4″ metal cylinder that was placedin a water bath at 180° F. to form set cement cylinders. Immediatelyafter removal from the water bath, destructive compressive strengthswere determined using a mechanical press in accordance with API RP10B-2. The results are set forth in the table below.

TABLE 1 24 Hr Ingredients Comp. Density Water Slag Pumice Lime Temp.Strength Sample (lb/gal) (gal/sk) (%) (%) (%) (° F.) (psi) 1 14.2 7.05100 — 10 180 314 2 14.2 6.85 90 10 10 180 359 3 14.2 6.55 75 25 10 180339 4 14.2 6.05 50 50 10 180 422 5 14.2 5.05 — 100 10 180 380

Based on the results of these tests, inclusion of pumice in the samplegeopolymer cement compositions had a significant impact on compressivestrength development. For example, increases in compressive strength ofat least about 5% (Sample 2) and up to least about 30% (Sample 4) wereobtained by replacing at least a portion of the pumice with slag. Asillustrated by the comparison of Samples 4 and 5, the combination ofpumice and slag appears to have a synergistic effect as Sample 4 with50% slag and 50% pumice had a higher compressive strength than Sample 1with 100% slag or Sample 2 with 100% pumice.

Example 2

The following series of tests was performed to evaluate thethickening-time response of including set retarders in geopolymer cementcompositions. Three different geopolymer cement compositions, designatedSamples 6-8, were prepared using the indicated amounts of water, slag,pumice, lime, a set retarder, and a fluid-loss-control additive. Theamounts of these components are indicated in the table below withpercent indicating the amount of the component by weight of the slag andpumice and gall on per sack (“gal/sk” indicating the gallons of therespective component per 94-pound sack of slag and pumice. The slag usedwas from LaFarge, Grand Chain, Ill. The lime used was hydrated lime fromTexas Lime Company, Cleburne, Tex. The pumice used was DS-200 from HessPumice Products, Inc., having an average particle size of less than 20microns. The set retarder was HR®-12 cement retarder from HalliburtonEnergy Services, Inc. The fluid-loss-control additive was Halad™-413from Halliburton Energy Services, Inc.

After preparation, the sample geopolymer cement compositions were testedto determine their thickening times at 140° F., which is the timerequired for the compositions to reach 70 Bearden units of consistency.The thickening-time tests were performed in accordance with API RP10B-2. The results are set forth in the table below.

TABLE 2 Thick Ingredients Time Sam- Density Water Slag Pumice LimeRetarder FLCA hr:min ple (lb/gal) (gal/sk) (%) (%) (%) (%) (%) (70 bc) 614.2 6.05 50 50 10 0.25 0.3 2:42 7 14.2 6.05 50 50 10 0.4 0.3 5:02 814.2 6.05 50 50 10 0.6 0.3 9:10

As illustrated, suitable thickening times can be obtained using setretarders in the sample geopolymer cement compositions. For example,thickening times in excess of 9 hours were obtained for Sample 8.

Example 3

The following series of tests was performed to evaluate the fluid lossof geopolymer cement compositions. Three different geopolymer cementcompositions, designated Samples 9-11, were prepared using the indicatedamounts of water, slag, pumice, lime, a set retarder, and afluid-loss-control additive. The amounts of these components areindicated in the table below with percent indicating the amount of thecomponent by weight of the slag and pumice and gallon per sack(“gal/sk”) indicating the gallons of the respective component per94-pound sack of slag and pumice. The slag used was from LaFarge, GrandChain, Ill. The lime used was hydrated lime from Texas Lime Company,Cleburne, Tex. The pumice used was DS-200 from Hess Pumice Products,Inc., having an average particle size of less than 20 microns. The setretarder was HR®-12 cement retarder from Halliburton Energy Services,Inc. The fluid-loss-control additive was Halad™-413 from HalliburtonEnergy Services, Inc.

After preparation, the geopolymer cement compositions were poured into apre-heated cell with a 325-mesh screen and a fluid-loss test wasperformed for 30 minutes at 1,000 psi at 190° F. in accordance with APIRP 10B-2.

TABLE 3 API Den- Fluid sity Ingredients Loss Sam- (lb/ Water Slag PumiceLime Retarder FLCA (cc/30 ple gal) (gal/sk) (%) (%) (%) (%) (%) min) 914.2 6.05 50 50 10 0.4 0.3  929¹  10 14.2 6.05 50 50 10 0.4 0.75 60 1114.2 6.05 50 50 10 0.4 1.0 54 ¹Calculated API Fluid Loss

As illustrated, suitable fluid-loss control can be obtained usingfluid-loss-control additives in the sample geopolymer cementcompositions. For example, API fluid loss of less than or equal to 60(cc/30 min were obtained for Samples 10 and 11.

It should be understood that the compositions and methods are describedin terms of “comprising,” “containing,” or “including” variouscomponents or steps, the compositions and methods can also “consistessentially of” or “consist of” the various components and steps.Moreover, the indefinite articles “a” or “an,” as used in the claims,are defined herein to mean one or more than one of the element that itintroduces.

For the sake of brevity, only certain ranges are explicitly disclosedherein. However, ranges from any lower limit may be combined with anyupper limit to recite a range not explicitly recited, as well as, rangesfrom any lower limit may be combined with any other lower limit torecite a range not explicitly recited, in the same way, ranges from anyupper limit may be combined with any other upper limit to recite a rangenot explicitly recited. Additionally, whenever a numerical range with alower limit and an upper limit is disclosed, any number and any includedrange falling within the range are specifically disclosed. Inparticular, every range of values (of the form, “from about a to aboutb,” or, equivalently, “from approximately a to b,” or, equivalently,“from approximately a-b”) disclosed herein is to be understood to setforth every number and range encompassed within the broader range ofvalues even if not explicitly recited. Thus, every point or individualvalue may serve as its own lower or upper limit combined with any otherpoint or individual value or any other lower or upper limit, to recite arange not explicitly recited.

Therefore, the present invention is well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as thepresent invention may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Although individual embodiments arediscussed, the invention covers all combinations of all thoseembodiments. Furthermore, no limitations are intended to the details ofconstruction or design herein shown, other than as described in theclaims below. Also, the terms in the claims have their plain, ordinarymeaning unless otherwise explicitly and clearly defined by the patentee.It is therefore evident that the particular illustrative embodimentsdisclosed above may be altered or modified and all such variations areconsidered within the scope and spirit of the present invention. Ifthere is any conflict in the usages of a word or term in thisspecification and one or more patent(s) or other documents that may beincorporated herein by reference, the definitions that are consistentwith this specification should be adopted.

1. A method of cementing comprising: providing a geopolymer cementcomposition comprising: a cementitious component consisting essentiallyof slag and pumice; lime selected from the group consisting of calciumoxide, calcium hydroxide, and a combination thereof; and water; andallowing the geopolymer cement composition to set.
 2. The method ofclaim 1, wherein the geopolymer cement composition has a density ofabout 12 pounds per gallon to about 20 pounds per gallon.
 3. The methodof claim 1, wherein the slag is present in an amount in a range of fromabout 40% to about 100% by weight of the cementitious component.
 4. Themethod of claim 1, wherein the pumice is present in an amount in a rangeof from about 0.1% to about 60% by weight of the cementitious component.5. The method of claim 1, wherein the slag is present in an amount in arange of from about 40% to about 60% by weight of the cementitiouscomponent, and wherein the pumice is present in an amount in a range offrom about 40% to about 60% by weight of the cementitious component. 6.The method of claim 1, wherein the cementitious component consists ofthe slag and the pumice.
 7. The method of claim 6, wherein thegeopolymer cement composition is free of any additional cementitiousmaterials.
 8. (canceled)
 9. The method of claim 1, wherein the lime ispresent in an amount in a range of from about 0.1% to about 25% byweight of the cementitious component.
 10. The method of claim 1, whereinthe geopolymer cement composition further comprises an additive selectedfrom the group consisting of a dispersant, a defoaming agent, astrength-retrogression additive, a set accelerator, a set retarder, aweighting agent, a lightweight additive, a gas-generating additive, amechanical-property-enhancing additive, a lost-circulation material, afiltration-control additive, a fluid-loss-control additive, a foamingadditive, a thixotropic additive, and any combination thereof.
 11. Themethod of claim 1, wherein the geopolymer cement composition furthercomprises an additive selected from the group consisting of crystallinesilica, amorphous silica, fumed silica, a salt, a fiber, a hydratableclay, calcined shale, vitrified shale, a microsphere, diatomaceousearth, metakaolin, ground perlite, rice husk ash, zeolite, a resin, andany combination thereof.
 12. The method of claim 1, further comprisingintroducing the geopolymer cement composition into a subterraneanformation.
 13. The method of claim 12, wherein introducing thegeopolymer cement composition into a subterranean formation comprisesintroducing the geopolymer cement composition into a well-bore annulus.14. The method of claim 1, wherein the geopolymer cement composition isused in a primary cementing operation.
 15. The method of claim 1,wherein inclusion of the pumice in the geopolymer cement compositionincreases the 24-hour compressive strength of the geopolymer cementcomposition at 180° F. in an amount of at least about 5% as compared toreplacement of the pumice with additional slag.
 16. A method ofcementing comprising: preparing a dry blend comprising lime and acementitious component comprising slag and pumice, wherein the lime isselected from the group consisting of calcium oxide, calcium hydroxide,and a combination thereof; combining the dry blend with water to from ageopolymer cement composition; introducing the geopolymer cementcomposition into a subterranean formation; and allowing the geopolymercement composition to set.
 17. The method of claim 16, wherein the slagis present in an amount in a range of from about 40% to about 60% byweight of the cementitious component, and wherein the pumice is presentin an amount in a range of from about 40% to about 60% by weight of thecementitious component.
 18. The method of claim 16, wherein thecementitious component consists of the slag and the pumice.
 19. Themethod of claim 18, wherein the geopolymer cement composition is free ofany additional cementitious materials.
 20. (canceled)
 21. The method ofclaim 16, wherein the lime is present in an amount in a range of fromabout 0.1% to about 25% by weight of the cementitious component.
 22. Themethod of claim 16, wherein introducing the geopolymer cementcomposition into a subterranean formation comprises introducing thegeopolymer cement composition into a well-bore annulus.
 23. The methodof claim 16, wherein inclusion of the pumice in the geopolymer cementcomposition increases the 24-hour compressive strength of the geopolymercement composition at 180° F. in an amount of at least about 5% ascompared to replacement of the pumice with additional slag.
 24. A methodof cementing comprising providing a geopolymer cement compositioncomprising: a cementitious component consisting of slag in an amount ina range of from about 40% to about 60% by weight of the cementitiouscomponent and pumice in an amount in a range of from about 40% to about60% by weight of the cementitious component, wherein the geopolymercement composition is free of any additional cementitious component;calcium hydroxide in an amount in a range of from about 0.1% to about20% by weight of the cementitious component; and water; introducing thegeopolymer cement composition into a well bore annulus in a subterraneanformation during a primary cementing operation; and allowing thegeopolymer cement composition to set wherein inclusion of the pumice inthe geopolymer cement composition increases the 24-hour compressivestrength of the geopolymer cement composition at 180° F. in an amount ofat least about 30% as compared to replacement of the pumice withadditional slag.
 25. (canceled)
 26. The method of claim 1, wherein thelime is the calcium hydroxide.
 27. The method of claim 16, wherein thelime is the calcium hydroxide.